This invention relates to solubilizing aqueous solutions of hydrophobic amines with cycloaliphatic amine cosolvent, and more particularly to aqueous solutions of hydrophobic amines operative as epoxy resin curing agents which yield highly cross linked, water resistant and abrasion resistant adhesive films.
Epoxy resin curing agent systems were traditionally mixed in an organic solvent base. Organic solvents have numerous problems including flammability, cost and the polluting effects of volatile organic component (VOC) release. Solvent recovery or vapor condensation after coating cure represent inefficient processes for coping with VOC release upon curing. Therefore, in order to comply with ever more stringent environmental regulations, there is a growing trend towards aqueous based epoxy resin curing agents. As a result, there has been considerable effort to develop water based epoxy resins and epoxy resin curing agents that upon mixing provide films having the same flexible, tough films obtained from solvent based mixtures.
The utilization of a surfactant to disperse hydrophobic epoxy resin curing agents in water have met with limited success. The films resulting from surfactant dispersions or emulsions generally exhibited poor chemical and water resistance, owing to the high concentration of surfactant contained within the films. Epoxy resin curing agents most often employed are amines such as polyamines or polyamides. Another approach to obtain aqueous solutions utilized hydrophilic amines as epoxy resin curing agents. Such amines have an affinity for water thus obviating the need for surfactants; however, the resulting cured epoxy films demonstrate poor water resistance as compared to solvent based films.
Superior epoxy resin curing agents, such as hydrophobic amines which form highly water resistant films, are not water soluble and require large quantities of cosolvent, surfactant or acid in order to create an aqueous dispersion or emulsion. This problem is exacerbated when the epoxy resin curing agent is a high equivalent weight amine which tends to impart desirable flexibility on a resulting cured film. Prior art attempts to form aqueous solutions of hydrophobic amines have utilized cosolvents including ethylene glycol ethers; polyoxyalkylene amines, U.S. Pat. No. 5,250,109; butyl cellosolve, U.S. Pat. No. 4,308,183; and the like which are described in U.S. Pat. No. 4,246,148; Bronsted and Lewis acids such as acetic acid and nitroparaffins. Unfortunately, cosolvents or acids tend to increase the concentration of VOCs. Entrapment of cosolvents or acids furthermore tends to detract from film barrier properties and increase the water sensitivity of the resulting cured film. Commercially available hydrophilic amines serve as reactive cosolvents for the dissolution of hydrophobic amines in water. Dytek A (DuPont) and EDR 148 (Texaco) are examples of common hydrophilic amines. Unfortunately, such hydrophilic amines support only limited addition of water to a hydrophilic/hydrophobic amine blend prior to phase separation of the hydrophobic amine from the aqueous portion.